Environmental effects on the mechanical properties of glass-fiber epoxy composite tubular specimens

The main objective of this experimental investigation was to study the effects of moisture absorption and exposure to elevated temperature on the mechanical properties of glass fiber reinforced epoxy composite tubes. Filament wound tubular composite specimens were immersed in distilled water at two different temperatures for approximately four months and their moisture absorption was recorded. The rate of moisture absorption was greater for the group of specimens immersed in distilled water at an elevated temperature (50 °C) than those at room temperature (∼20 °C). Multi-axial tests were performed subsequently, and it was observed that for all biaxial stress ratios, strength and stiffness decreased to some extent with the presence of moisture and increasing temperature. Strains parallel and transverse to the fibers at functional failure (leakage) showed little variation in the presence of moisture and temperature with the exception of pure hoop loading. Microscopically, the greatest water damage was apparent in the matrix and at the fiber–matrix interface where there was less resin adhesion to the fibers with increasing water temperature. Fiber strength was also negatively affected, possibly due to either leaching out of the glass fibers interface layer or glass fiber embrittlement, and less effective bonding and load distribution at the fiber–matrix interface.